Peripheral blood cells and certain lymphoblastoid tissue culture cell lines secrete a variety of soluble substances called lymphokines which in turn activate other cells in the body. One of these lymphokines, Macrophage Activation Factor (MAF) has the ability to induce resting macrophages to become cytotoxic to tumor cells. There has not been any clinical trials of MAF due to difficulties in obtaining this material in large enough amounts and of high enough purity. Production of human MAF of high quality would allow one to study the primary amino acid sequence structure of MAF its subunit organization, and delineate the active binding Site(s) in the molecule. MAF has been isolated from a Burkitt's lymphoma cell line, Namalva, by standard proteins chemistry techniques. These include G-100 chromatography and affinity chromatography over mixed brais gangliosides. we have currently made arrangements to obtain the culture supernatant from 500 liters of Namalva cells and to begin various tractionations procedures which will include concentration by TCA precipitation biological activity for MAF will be assayed by measuring cytotoxicity of tumor cell targets culture with MAF-treated macrophages.